Age 10-11 I was bullied by a group of girls and the reason I was bullied by them was because apparently I was a bully and I was getting my 'karma'

Anyways, they bullied me - they left me out, would barge past me, hide my things, call me names and so on and so forth, and the excuse was because I was a bully so now they are bullying me.

Age 11-12 I was "bullied" by my friends in the sense they would say things like make fun of me

When I was 16, I was bullied by some girls who were not my friends- they would make fun of me, hide my things, say I smelt of fish, laugh/mock me and the girls who were supposed to be my friends did not defend me at all.
It ended with me crying in front of the whole class, and the girls getting in trouble for bullying.

I feel ashamed that I was bullied, that they saw me cry, I am upset and angry at the years wasted being bullied and how they made me feel. I feel awkward encase I ever see them again, especially as they would deny everythin
I have not been bullied since age 16 (and never will) as I DO NOT STAND FOR IT. If anyone so much as tries it, I let them know what is up

You said it yourself: It was payback.

I bet you stopped bullying other people after that experience.